Strong language skills are foundational for the development of literacy. This project investigates how grammatical development relates to literacy development in 9- to 10-year-old monolingual Spanish, monolingual English, and Spanish-English bilingual children by assessing comprehension of complex grammatical structures mastered through increased exposure to written language at school. To appropriately measure children's later grammatical development we need specific and theoretically-motivated diagnostic tests of complex syntactic knowledge, which we currently lack. Existing tools normed for monolingual English and Spanish do not assess complex syntax adequately, and schools lack precise measures of grammatical development they can use to identify the factors contributing to children's language and literacy outcomes. Valid assessment instruments are vital to advance research and educational practices with typically-developing monolingual and bilingual speakers schooled in one or two languages. Our innovation is the creation of new theoretically-motivated linguistic measures in Spanish and English informed by linguistic theory and language acquisition research to assess auditory comprehension of complex grammatical structures in Spanish and English that are crucial for literacy development. The goal of this project is to validate new picture-based comprehension tasks with 100 monolingual and 50 bilingual speakers of Spanish and of English, 9- to10-year old (75 children, 75 adults). Specific Aim 1 examines the validity of the new language measures in Spanish testing verbal passives, relative clauses, and pronoun interpretation and their relationship to global proficiency, literacy and cognitive measures. Specific Aim 2 examines the validity of the new measures in English testing the same structures. To examine criterion-related validity, scores on the new language tasks will be correlated with established global proficiency measures--the three Spanish and three English subtests from the Woodcock Johnson IV Tests of Oral Language, and established literacy measures: the passage comprehension and reading fluency sections in Spanish from the Batera III Woodcock-Muoz, and the equivalent English subtests from the Woodcock-Johnson IV Achievement Test. To determine whether potential difficulty with complex grammar comprehension by the bilingual children is related to phonological working memory or to incomplete acquisition of Spanish and/or English, performance on the new linguistic tasks will be correlated with scores on established cognitive measures of executive functioning and phonological working memory. Once validated, our new linguistically informed tests will allow us to make progress methodologically and theoretically, to understand typically-developing monolingual and dual language profiles, and to address the inextricable links between complex grammar, cognitive functioning, and written language. The knowledge gained from this project will be critical for developing effective assessment, instruction, and intervention strategies to promote robust language and literacy skills and academic success in the Hispanic population.